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    <p>There are many ways to write this kind of thing. </p> <p>A flexible approach is separate "actions" from "sequence", allowing :</p> <ul> <li>functions a, b, c to initiate an asynchronous (ajax) action, with no knowledge of how they are to be sequenced</li> <li>a, b, c to be reusable, as part of one or more sequences or individually, as required.</li> </ul> <p>Here's a way to code this approach, using <code>.then()</code> exclusively for the chaining logic :</p> <pre><code>function a() { return $.post(...).then(function(result) { if(result) return result;//continue on "success" path. else return $.Deferred().reject('a').promise();//convert success to failure. }, function() { return 'a';//continue on failure path. }); } function b() { return $.post(...).then(function(result) { if(result) return result;//continue on "success" path. else return $.Deferred().reject('b').promise();//convert success to failure. }, function() { return 'b';//continue on failure path. }); } function c() { return $.post(...).then(function(result) { if(result) return result;//continue on "success" path. else return $.Deferred().reject('c').promise();//convert success to failure. }, function() { return 'c';//continue on failure path. }); } a().then(b).then(c).then(function() { console.log("successful"); }, function(id) { console.log("failed: " + id); }); </code></pre> <p>Alternatively, if you want to have a single asynchronous function, <code>a</code>, called from within a loop then the code could be something like this :</p> <pre><code>function a(obj) { return $.post(...).then(function(result) { if(result) return result;//continue on "success" path. else return $.Deferred().reject(obj.id).promise();//convert success to failure. }, function() { return obj.id;//continue on failure path. }); } var data = [{id:'A', param1:1235, param2:3214}, {id:'B', param1:5432, param2:9876}]; //Note how IDs are included so these data objects can be identified later in failure cases. var dfrd = $.Deferred();//starter Deferred for later resolution. var p = dfrd.promise();//A promise derived from the starter Deferred, forming the basis of a .then() chain. //Build a .then() chain by assignment $.each(data, function(i, obj) { p = p.then( function() { return a(obj); });//By not including a fail handler here, failures will pass straight through to be handled by the terminal .then()'s fail handler. }); //Chain a terminal .then(), with success and fail handlers. p.then(function() { console.log("successful"); }, function(id) { console.log("failed: " + id); }); dfrd.resolve();//Resolve the starter Deferred to get things started. </code></pre>
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